Human medicine used to be the major user of antibiotics. Now it is farmers. Antibiotics are used on a tremendous scale in factory farming to suppress the spread of diseases amongst animals which are housed so densely. Whilst this means that the animals are generally disease-free, the advent of a new resistant strain of infectious organism can wipe out entire houses of animals. Since 2017, animals consume more antibiotics than humans. About 80% of the antibiotics used in agriculture are added to poultry, hog, and cattle feed, not to treat sick animals but to promote growth and prevent disease; so bacteria in and around the animals are regularly exposed to the drug, which gives rise to drug-resistant superbugs. This indiscriminate and non-essential use of antibiotics in agriculture dangerously increases the possibility that these antibiotics (and other closely related ones) will be ineffective when needed to treat people. Overuse of antibiotics in agriculture has led to serious antibiotic-resistance problems in foods. Strains of Salmonella and other disease-causing organisms found in raw and undercooked meat are increasingly resistant to several antibiotics. One strain of Salmonella that is resistant to five different antibiotics increased from 0.6% of specimens tested in 1980 to 34% in 1997.
In 2016, researchers calculated that worldwide about 63,000 tons of antibiotics are fed to chickens, pigs, and cattle each year. Furthermore, they predicted that this number will rise by 67 percent, or 106,000 tons, by 2030. Nearly 80 percent of the antibiotics sold in the United States are also used in meat and poultry production.